The present invention generally relates to an apparatus capable of simultaneous acquisition of data from multiple molecular sensing modalities, for example and not by way of limitation, a labeled process (such as a fluorescence process) and a label-free process (such as an interferometric process).
Generally, labeled and label-free detection modalities for molecular sensing possess complimentary advantages and drawbacks. For instance, label based sensing systems are not susceptible to background effects as much as label-free systems. Susceptibility to background effects often limits the sensitivity of label-free systems. On the other hand, labeled systems such as fluorescence, which is the most common molecular detection modality in use today, suffer from low photon fluxes which limit their sensitivity, while label-free sensing systems (e.g., the Quadraspec biological compact disc system, such as described in the U.S. Pat. No. 6,685,885) have photon fluxes that are several orders of magnitude higher.
Fluorescence label based systems suffer from additional problems such as photobleaching, which limits the ability to perform time-resolved studies beyond a certain length of time. Label-free systems generally do not suffer from such problems.
Label based systems require an additional chemical processing step of attaching the “label” molecule to the molecule of interest. This process, in addition to increased processing time and cost, can alter the behavior of the molecules of interest. Label-free systems do not require this additional processing step.
In spite of drawbacks such as the ones described above, fluorescent label based detection remains a widely used technology for molecular sensing applications, such as immunosensing and drug discovery, and possesses high sensitivity, especially in the detection of low molecular weight analytes and even single molecule detection.
There are two main reasons for the observed performance of fluorescent label based systems compared to current label-free technologies. First, as mentioned earlier, fluorescent label based systems are not as susceptible to variations in background effects as label-free systems. Susceptibility to background effects can limit the sensitivity of label-free systems. Second, signal transduction in label-free systems is based on some physical property of the molecule of interest, which is often related to its molecular size. Coupled with the background problem, this molecular size dependency restricts the range of molecular size that can be detected reliably with label-free systems. For example, detection of low-molecular weights in immunoassay continues to be a challenge for many label-free systems and they try to get around the molecular size dependency through alternate assay formats such as reverse phase or inhibition assays. While the success of such approaches in circumventing the molecular weight dependency has been demonstrated, these approaches may not always be feasible. Label based systems on the other hand rely only on the properties of the “label” molecule and consequently work independent of the size of the molecule of interest. Thus they work equally well for large as well as small molecules and meet the demand for low molecular weight detection in many application areas.
Even though fluorescent based systems have good performance compared to current label-free systems, the increasing demand for multiplexing is expected to put a significant strain on fluorescent based systems. This is because each molecule of interest requires a unique label. Although some approaches, such as Quantum Dots, have been proposed to address the “unique label” problem, considerable understanding of their interaction with bio-molecules will need to be built for them to emerge as a ubiquitous molecular sensing format. Label-free systems do not suffer from this limitation and as a result are attractive from the multiplexing point of view.
From the items described above, it can be seen that the labeled and label-free molecular detection modalities can provide complimentary performance attributes. However, commercially available molecular sensing platforms do not exploit these complementary properties. Integrating these complementary molecular sensing modalities in a single platform can enhance the capabilities of either mode by providing capability to perform low molecular weight detection with high sensitivity as well as the ability of multiplexing without label limitations for suitable applications.
With this objective in mind, exemplary embodiments of systems incorporating complementary molecular sensing modalities in a single platform are disclosed below. One embodiment integrates fluorescence based detection (most widely used label based detection) and interferometric based detection (most inherently sensitive label-free technology) into a single instrument. This instrument is capable of simultaneous data acquisition from both channels. The acquired data from both channels can be analyzed, and biologically relevant information, such as the amount of bound protein, can be extracted.